Noncoding RNAs Regulating p53 and c-Myc Signaling. In: Song E, editor. The Long and Short Non-coding RNAs in Cancer Biology. Singapore: Springer; 2016. pp. 337-65. [DOI: 10.1007/978-981-10-1498-7_13]

MYC Oncogene: A Druggable Target for Treating Cancers with Natural Products

Various diseases, including cancers, age-associated disorders, and acute liver failure, have been linked to the oncogene, MYC. Animal testing and clinical trials have shown that sustained tumor volume reduction can be achieved when MYC is inactivated, and different combinations of therapeutic agents including MYC inhibitors are currently being developed. In this review, we first provide a summary of the multiple biological functions of the MYC oncoprotein in cancer treatment, highlighting that the equilibrium points of the MYC/MAX, MIZ1/MYC/MAX, and MAD (MNT)/MAX complexes have further potential in cancer treatment that could be used to restrain MYC oncogene expression and its functions in tumorigenesis. We also discuss the multifunctional capacity of MYC in various cellular cancer processes, including its influences on immune response, metabolism, cell cycle, apoptosis, autophagy, pyroptosis, metastasis, angiogenesis, multidrug resistance, and intestinal flora. Moreover, we summarize the MYC therapy patent landscape and emphasize the potential of MYC as a druggable target, using herbal medicine modulators. Finally, we describe pending challenges and future perspectives in biomedical research, involving the development of therapeutic approaches to modulate MYC or its targeted genes. Patients with cancers driven by MYC signaling may benefit from therapies targeting these pathways, which could delay cancerous growth and recover antitumor immune responses.

Ribosome-Directed Therapies in Cancer

The human ribosomes are the cellular machines that participate in protein synthesis, which is deeply affected during cancer transformation by different oncoproteins and is shown to provide cancer cell proliferation and therefore biomass. Cancer diseases are associated with an increase in ribosome biogenesis and mutation of ribosomal proteins. The ribosome represents an attractive anti-cancer therapy target and several strategies are used to identify specific drugs. Here we review the role of different drugs that may decrease ribosome biogenesis and cancer cell proliferation.

MYC: a multipurpose oncogene with prognostic and therapeutic implications in blood malignancies

MYC oncogene is a transcription factor with a wide array of functions affecting cellular activities such as cell cycle, apoptosis, DNA damage response, and hematopoiesis. Due to the multi-functionality of MYC, its expression is regulated at multiple levels. Deregulation of this oncogene can give rise to a variety of cancers. In this review, MYC regulation and the mechanisms by which MYC adjusts cellular functions and its implication in hematologic malignancies are summarized. Further, we also discuss potential inhibitors of MYC that could be beneficial for treating hematologic malignancies.

MicroRNAs and long non-coding RNAs as novel regulators of ribosome biogenesis

Ribosome biogenesis is the fine-tuned, essential process that generates mature ribosomal subunits and ultimately enables all protein synthesis within a cell. Novel regulators of ribosome biogenesis continue to be discovered in higher eukaryotes. While many known regulatory factors are proteins or small nucleolar ribonucleoproteins, microRNAs (miRNAs), and long non-coding RNAs (lncRNAs) are emerging as a novel modulatory layer controlling ribosome production. Here, we summarize work uncovering non-coding RNAs (ncRNAs) as novel regulators of ribosome biogenesis and highlight their links to diseases of defective ribosome biogenesis. It is still unclear how many miRNAs or lncRNAs are involved in phenotypic or pathological disease outcomes caused by impaired ribosome production, as in the ribosomopathies, or by increased ribosome production, as in cancer. In time, we hypothesize that many more ncRNA regulators of ribosome biogenesis will be discovered, which will be followed by an effort to establish connections between disease pathologies and the molecular mechanisms of this additional layer of ribosome biogenesis control.

Chronic Hexavalent Chromium Exposure Induces Cancer Stem Cell-Like Property and Tumorigenesis by Increasing c-Myc Expression

Hexavalent chromium [Cr(VI)] is one of the most common environmental carcinogen causing lung cancer in humans; however, the mechanism of Cr(VI) carcinogenesis remains elusive. Cancer stem cells (CSCs) are considered as cancer initiating and maintaining cells. Ours and other recent studies showed that chronic Cr(VI) exposure induces CSC-like property representing an important mechanism of Cr(VI) carcinogenesis. However, how Cr(VI) exposure induces CSC-like property remains largely unknown. In this study, we found that stably knocking down the expression of c-Myc, a proto-oncogene and one of key stemness factors playing critical roles in cancer initiation and progression, in Cr(VI)-transformed human bronchial epithelial cells [BEAS-2B-Cr(VI)] significantly decreased their CSC-like property and tumorigenicity in mice. Moreover, stably knocking down c-Myc expression in parental nontransformed BEAS-2B cells significantly impaired the capability of chronic Cr(VI) exposure to induce CSC-like property and cell transformation. It was also found that stably overexpressing c-Myc alone in parental nontransformed BEAS-2B cells is capable of causing CSC-like property and cell transformation. Mechanistic studies showed that chronic Cr(VI) exposure increases c-Myc expression by down-regulating the level of microRNA-494 (miR-494). It was further determined that overexpressing miR-494 significantly reduces Cr(VI)-induced CSC-like property, cell transformation, and tumorigenesis mainly through down-regulating c-Myc expression. Together, these findings indicate that chronic low dose Cr(VI) exposure induces CSC-like property and tumorigenesis by increasing c-Myc expression through down-regulating the level of miR-494, revealing an important role of the proto-oncogene c-Myc in Cr(VI) carcinogenesis.

Reduced P53 levels ameliorate neuromuscular junction loss without affecting motor neuron pathology in a mouse model of spinal muscular atrophy

Spinal Muscular Atrophy (SMA) is a childhood motor neuron disease caused by mutations or deletions within the SMN1 gene. At endstages of disease there is profound loss of motor neurons, loss of axons within ventral roots and defects at the neuromuscular junctions (NMJ), as evidenced by pathological features such as pre-synaptic loss and swelling and post-synaptic shrinkage. Although these motor unit defects have been widely described, the time course and interdependancy of these aspects of motor unit degeneration are unclear. Recent reports have also revealed an early upregulation of transcripts associated with the P53 signalling pathway. The relationship between the upregulation of these transcripts and pathology within the motor unit is also unclear. In this study, we exploit the prolonged disease timecourse and defined pre-symptomatic period in the Smn^2B/- mouse model to perform a temporal analysis of the different elements of motor unit pathology. We demonstrate that NMJ loss occurs prior to cell body loss, and coincides with the onset of symptoms. The onset of NMJ pathology also coincides with an increase in P53-related transcripts at the cell body. Finally, using a tamoxifen inducible P53 knockout, we demonstrate that post-natal reduction in P53 levels can reduce NMJ loss, but does not affect other aspects of NMJ pathology, motor neuron loss or the phenotype of the Smn^2B/- mouse model. Together this work provides a detailed temporal description of pathology within motor units of an SMA mouse model, and demonstrates that NMJ loss is a P53-dependant process. This work supports the role for P53 as an effector of synaptic and axonal degeneration in a die-back neuropathy.

Long noncoding RNA EMS connects c-Myc to cell cycle control and tumorigenesis

Deregulated expression of c-Myc is an important molecular hallmark of cancer. The oncogenic function of c-Myc has been largely attributed to its intrinsic nature as a master transcription factor. Here, we report the long noncoding RNA (lncRNA) E2F1 messenger RNA (mRNA) stabilizing factor (EMS) as a direct c-Myc transcriptional target. EMS functions as an oncogenic molecule by promoting G1/S cell cycle progression. Mechanistically, EMS cooperates with the RNA binding protein RALY to stabilize E2F1 mRNA, and thereby increases E2F1 expression. Furthermore, EMS is able to connect c-Myc to cell cycle control and tumorigenesis via modulating E2F1 mRNA stability. Together, these findings reveal a previously unappreciated mechanism through which c-Myc induces E2F1 expression and also implicate EMS as an important player in the regulation of c-Myc function.

TRMP, a p53-inducible long noncoding RNA, regulates G1/S cell cycle progression by modulating IRES-dependent p27 translation

The tumor suppressor p53 plays a pivotal role in the protection against cancer. Increasing evidence suggests that long noncoding RNA (lncRNA) plays an important role in the regulation of the p53 pathway, however, the detailed mechanisms remain to be further elucidated. In this study, we report a new p53-inducible lncRNA that we termed TRMP (TP53-regulated modulator of p27). As a direct transcriptional target of p53, TRMP plays an unexpected pro-survival function. Knockdown of TRMP inhibits cell proliferation by inducing a G1 cell cycle arrest. Mechanistically, TRMP suppresses internal ribosomal entry site (IRES)-dependent translation of p27 by competing p27 mRNA for polypyrimidine tract-binding protein 1 (PTBP1) binding. Furthermore, TRMP is able to regulate cell proliferation, G1/S cell cycle progression, and tumor xenograft growth via the inhibition of p27. Taken together, these findings suggest lncRNA as a new layer to fine-tune the p53 response and reveal TRMP as an important downstream effector of p53 activity.